1. Field of the Invention
This invention relates to a derailleur arrangement, in particular for bicycles, comprising a driving sprocket unit and a driven sprocket unit, a well as a chain connecting these two sprocket units to one another, whereby at least one of the sprocket units is designed as a multisprocket unit with at least two sprockets, namely a larger sprocket and a smaller sprocket. In addition, the two sprockets of the multisprocket unit each typically have a number of teeth and a corresponding number of spaces formed between each pair of teeth. In addition, the chain is typically formed by successive chain links and by inner and outer link plate pairs in alternating sequence between the chain links. In addition, to shift the chain between the two sprockets of the multisprocket unit, there is typically a shifter in an approach area in which, in the normal direction of circulation of the chain and of the sprockets, the chain approaches the multisprocket unit, and this shifter is designed to impart motions to the chain in a direction parallel to the axis of the multisprocket unit.
In addition, when the chain is shifted between the sprockets of the multisprocket unit, a chain transfer segment is typically formed between the sprocket from which the chain is being transferred and the sprocket to which the chain is being transferred, which chain transfer segment traverses the circulation area of the multisprocket unit from the chain approach area to a chain runout area of the multisprocket unit. In addition, the chain transfer segment typically extends opposite to the normal direction of circulation of the sprocket set, from a chain link which is the last chain link engaged between two final teeth of a final pair of teeth of the sprocket from which the chain is being transferred, to a chain link which is the first link engaged between two first teeth of a first pair of teeth of the sprocket to which the chain is being transferred, and whereby in at least one chain transfer circumferential area of the multisprocket unit, corresponding to the chain shifting in the shifting direction from a smaller sprocket to a larger sprocket, design measures are applied to the sprockets in this chain transfer circumferential area, to facilitate the shifting of the chain between the two sprocket wheels, at least in the shifting direction from the smaller sprocket to a larger sprocket, and to define the path of the corresponding chain transfer segment.
2. Background Information
DE-C2 28 37 270 discloses a known bicycle derailleur with a chain and a set of sprockets, the set of sprockets having at least one smaller sprocket and at least one larger sprocket oriented coaxially to and at some distance from this larger sprocket. The larger sprocket has at least two teeth which are designed to facilitate engagement with the chain. During the shifting process, the chain must apparently be engaged essentially at all times with, one one hand, a link pin between two teeth of a pair of teeth of the larger sprocket, and, on the other hand, with a link pin between two teeth of a pair of teeth of the smaller sprocket, and thereby, the chain, i.e. in its path between these two link pins, it must apparently extend tangentially to the smaller sprocket and bridge the distance between the pairs of teeth of the two sprockets. The distance from the midpoint of the one pair of teeth, between which the one link pin is engaged, and the midpoint of the other pair of teeth, between which the other link pin is engaged, must thereby apparently be an integral multiple of the chain pitch, and the two teeth of the pair of teeth of the larger chain wheel must apparently be designed or oriented to facilitate their engagement with the chain.
In the known embodiment, there are teeth over essentially the entire circumference of the larger sprocket. Some of the teeth are shortened to facilitate the transfer of the chain. On the larger sprocket, there are two pickup teeth, possibly safety or guide teeth, one of which is designed to be engaged between two inner link plates, and the other to be engaged between two outer link plates. Both pickup teeth have engagement flanks for the engagement with the link pins. Both pickup teeth are made thinner by setting the teeth toward the smaller sprocket. On account of this thinning, which is designed to facilitate the transfer of the chain from the smaller sprocket to the larger sprocket, there tends hardly to be essentially any possibility of applying additional design measures to these teeth, to facilitate the transfer from the larger sprocket to the smaller sprocket.